Think about what you said, a 45 round is larger in diameter than a 9mm so right of the bat your incorrect about the amount of rounds. The average 9mm magazine hold 16 rounds, where the average 45 magazine holds 10. It only takes one round to take a life from either weapon, so in a tactical situation I would much rather have more rounds.
Having said all of that I like 45 rounds, I have nothing against them. But they are way more expensive and you carry less of them. Hell a .22 caliber round will take a life easily, the entire scenario depends entirely on your training and your nerves in the heat of the moment.